DE4103145C2 - - Google Patents
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- DE4103145C2 DE4103145C2 DE19914103145 DE4103145A DE4103145C2 DE 4103145 C2 DE4103145 C2 DE 4103145C2 DE 19914103145 DE19914103145 DE 19914103145 DE 4103145 A DE4103145 A DE 4103145A DE 4103145 C2 DE4103145 C2 DE 4103145C2
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- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through the meter in a continuous flow
- G01F1/66—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through the meter in a continuous flow by measuring frequency, phaseshift, or propagation time of electromagnetic or other waves, e.g. ultrasonic flowmeters
- G01F1/662—Constructional details
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/18—Methods or devices for transmitting, conducting, or directing sound
- G10K11/22—Methods or devices for transmitting, conducting, or directing sound for conducting sound through hollow pipes, e.g. speaking tubes
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2291/00—Indexing codes associated with group G01N29/00
- G01N2291/02—Indexing codes associated with the analysed material
- G01N2291/028—Material parameters
- G01N2291/02836—Flow rate, liquid level
The invention relates to an ultrasonic probe according to the preamble of the patent Claim 1.
For example, ultrasound probes find their application in the medical field Sonography.
There are known so-called ultrasonic pulse echo methods in which ultrasound pulses are irradiated into tissue and the signals reflected by tissue are registered in order, for. B. from the time course of the reflected signals on the depth structure of the tissue to close. In the so-called ultrasonic double method, the shift in the frequency of the reflected signal with respect to. The irradiated is measured in order for. B. to determine the speed of the reflective structure. Ultrasonic pulses are usually used with a carrier frequency f₀, a pulse duration T p and a repetition rate f w (pulses per second).
To achieve a high spatial resolution in these methods, is a short sound wave length λ₀ or a high carrier frequency f₀ required (λ₀ = c₀ / f₀; λ₀: mean sound wavelength, c₀: mean sound velocity of the medium for the excited wave type). On the other hand, the Carrier frequency f₀ not be too high, because otherwise the attenuation of the sound waves becomes too strong through absorption or scattering: For many media takes the ultrasonic absorption approximately in the relevant frequency ranges with the second and the scatter even with the fourth power the frequency too. In medical sonography one is therefore generally limited to the frequency range of a few MHz. For investigations, where only a small penetration depth is required, can However, the frequency may be up to 20 MHz, z. B.G.S. Werner et al., "Intravascular Ultrasound Diagnosis", Dtsch. med. Wschr. 115, 1259 (1990).
In the pulse echo method, it is favorable to use pulses with short duration T p , because z. B. the depth of field of the probe is also limited by the spatial pulse length L p ≈ c₀ · T p . On the other hand, it does not make sense to use pulses with a duration T p <1 / f, because then no gain in spatial resolution is obtained.
The Doppler methods generally require a low spatial resolution, but it depends on a precise measurement of speeds. As a rule of thumb that the accuracy of measurement .DELTA.c ≈ c₀ · Δ f / f₀ scaled, wherein the frequency width Δ f of the sound impulses is inversely related to the pulse duration, Δ f ≈ 1 / T p and Δ c ≈ c₀ / (T p · f₀) applies: high frequencies and long pulses can be so cheap. In extreme cases, even continuous wave signals with T p »1 / f₀ are used, a spatial resolution is then only due to the directivity of the transducer.
The transducer of an ultrasound probe usually consists of an imaging device System, the so-called. Ultrasonic straightening element and directly on this attached electromechanical ultrasonic transducers. In the simplest case a transducer has a substantially homogeneous straightening element whose Type. Transverse dimensions, denoted by D, are large in comparison to the mean sound wave length in the tissue to be examined: D <λ₀. Then the directional element has a directional characteristic, d. H. the radiated Ultrasonic energy is on a narrow area around its axis and he receives essentially only sound, that of a close Range goes out around its axis. Is the straightening z. B. a rotary piston radiator, is the full opening angle ("3 dB width") for the "main lobe" in radians ΔR ≈ 0.52 · (λ₀ / D). A description of the Rotary piston radiator can be found z. B. in H. Kuttruff, "Physics and Technology of ultrasound ", S. Hirzel Verlag, 1988 (ISBN: 3-7776-0427-5) Known how to get the directional characteristic of ultrasonic straightening elements as the rotary piston radiator improved, z. B. by using focusing Elements. This can be along the axis of the straightening elements areas for the ultrasound examination (areas of increased Ultrasonic intensity in the radiation or when receiving) to this z. B. to be able to study with Doppler method with long pulses.
The investigation of spatial structures requires scanning in or two directions. In the simplest case, this is a single transducer guided along the body surface, the measurement results to a two-dimensional Picture (track and depth) are joined together. An overview scanning methods can be found in R. Millner (ed.), "Ultraschalltechnik- Basics and Applications ", Physik-Verlag Weinheim, 1987 (ISBN: 3-87664- 106-3).
Percutaneous investigations of deep structures have, among other things, the disadvantage that the ultrasonic waves attenuated too much at the examination site are, whereby the spatial resolution is reduced. Next can be ultrasonic waves only poorly penetrate bone or lung tissue. Here it is known, ultrasonic directors and transducers at the distal end of probe tubes to install. These usually flexible probe tubes or catheters One can introduce into the patient and examine the intracorporeal carry out.
In medicine, such ultrasonic probes with a variety of treatment devices combined. The US-PS 48 87 605 describes z. B. one Catheter for laser angioplasty, in which an optical fiber for Transmission of laser radiation is located. The transducer (straightening element with Transducer) at the distal end allows control of a laser ablation process.
Particularly advantageous is the combination of sound probes with endoscopes (Endosonographen). The sound probe can complement the endoscope, such as from EP-PS 00 46 987 is known. There the sonograph serves for the determination the distance of the targeted object from the observation window, so Its size can be determined exactly. The sonograph can also be independent Diagnostic device of the endosonograph. With an introduced Transducer can be z. B. surrounding the probe head, opaque Examine tissue while using the endoscope of the probe head in the patient is precisely positioned. Mostly the endoscopes are in straight view and The sonographs operated in a side view, but there are many other versions. For example, EP-PS 00 61 332 in Endosonograph describes in which at the probe head an additional peripheral window for the optical side view is located.
To reach a spatial resolution with the ultrasound probes, several come Procedure in question. DE-OS 39 10 336 describes z. For example, a sector scan method: The cylindrical probe head has a circumferential direction Radial ultrasound beam window showing an azimuthal sector scan allowed by almost 360 °. These are, however, electric drives in Probe head necessary, whereby the probe head is relatively clunky, such probes are used for examinations of the gastrointestinal tract Question. The probe can also be z. B. a hollow shaft rotatable from the outside be, as known from DE-OS 38 16 982.
The known transducers (straightening elements with transducers) of the ultrasound probes have z. B. for intracorporeal applications significant disadvantages:
- - Ultrasonic transducers are temperature sensitive. This creates Problems with sterilizability.
- - Ultrasonic transducers (often piezoceramics) develop heat in the probe head, which can be difficult to dissipate because of the compact design.
- - The probes are relatively thick, so their use z. B. in the Arthroscopy and bronchoscopy considerably limited.
- - The operation of the converter requires relatively high voltages. They must therefore be well insulated. If probe heads z. B. For cleaning, there are cracks through which Body fluid can penetrate and cause a short circuit.
To solve these problems z. B. proposed in DE-OS 32 19 118, to attach special electrical contacts on the probe head, which is a simpler allow mechanical replacement of components. In the DE-OS 35 37 904 is proposed, the ultrasonic transducer in the probe head of the Decouple control and display units. This decoupling should be inductive, capacitive or via optical couplers. These devices have the Deficiencies in the catheter-guided sonography but not resolved.
The US-PS 44 07 294, 44 28 379 and 44 31 006 describe z. B. as hollow needles executed lancets, which are stung through the skin and into the Sound conductor, preferably made of steel, inserted and pushed through to the top be used to examine the tissue at the top. It is with This procedure difficult to obtain ultrasound images - for investigation extensive structures would be necessary for each examination point Restart the lancet. Next it is a problem, lancet and sound waveguide acoustically decoupled - by the coupling of sound become z. B. falsifies the signals. That is why you are in the hollow needle sound-absorbing layers, this makes the needle thick and its applicability limited. Furthermore, the sound conductor is too rigid and too short to be used in catheters.
WO-A-87 01 269 describes a method for transmitting ultrasound images, in the sound waves with fibers or fiber bundles of one Transducers outside the body to an organ in the body and the reflected Waves are retransmitted again. Provided, the fiber or fiber bundle is the organ to be examined contacted with this method, at best, the contact with the fiber or fiber bundle end directly adjacent thin tissue layer examine. The investigation of deep structures is not possible. Flatly extended Images could only be obtained by using fiber bundles, wherein the imageable surface is defined by the cross-sectional area of the fiber bundle is limited. A disadvantage of the design as a fiber bundle is that in specified frequency range of less than 10 MHz the sound wave length still so great that between the fibers of the bundle a strong overcoupling of sound energy that destroys the image information. We found that in fiber bundles by the relative movement of the fibers a very strong damping and dispersion of sound energy occurs. From DE-OS 20 15 698 an ultrasonic transmission system is known consisting of a converter located in an operating unit at the proximal end of the transfer device, a consumer, such as, for example, by means of ultrasound powered tools, located at the distal end of the transmission device, and a Sound waveguide, which sound waves from the transducer to the Consumer transfers. The sound waveguide according to DE-OS 20 15 698 consists of a bundle of wires, in particular more than 100 Wires. A disadvantage of this sound waveguide and thus on the known transmission device is that this fiber bundle not with Axialwellen high power can be applied. At high Sound intensities, the thin fibers are destroyed by buckling. Furthermore, in such fiber bundles, as already described above, due to the relative movement of the fibers during vibration a strong Friction of the fibers connected to each other with a strong sound absorption on. Also, the document no evidence to be taken, such as losses can be reduced due to the radiation of radial waves.
The invention has for its object to provide an ultrasonic probe with high Spatial resolution and great depth of field to create the electrically safe is the heat in the probe head is low and the one compact design allows. In addition, the ultrasound probe is a high transmission efficiency, d. H. only small losses of sound energy by absorption in the sound waveguide or radial radiation, have and especially suitable for use in medical sonography his.
This object is achieved by the ultrasonic probe described in claim 1 solved.
In the ultrasonic probe according to the invention, the sound waves with Transducers are generated at the proximal end of the probe and via suitable sound waveguides (SWL) to straightening elements at the distal end of the probe (probe head) transfer.
The removal of the transducers from the probe head has the advantage that electrical supply lines to the probe head unnecessary. The probe is through electrically safe and the heat development in the probe head is small. at the construction of the straightening elements, the converter can be disregarded remain: This can be in a narrow probe head straightening elements accommodate with a high directivity. Scanning can be done by suitable mechanical, pneumatic and Ä. Devices take place in the probe head. The Probes become thinner and are suitable for use in narrow vessels in narrow vessels. The use of the sound waveguide described in claim 1 Ensures that even very short sound pulses without effective temporal or frequency deformation can be transmitted.
The use of the SWL designed according to the invention furthermore ensures that even very short sound pulses without effective damping or effective temporal or frequency deformation can be transmitted. The diameter of the sound waveguide according to the invention, however, is so small that the sound waveguide itself has no directivity. For this reason, the use of a straightening element on the probe head is required. The straightening element also has the task of coupling the sound waves to promote the medium to be examined - sound waveguide usually leave no efficient coupling to the examined Medium too.
In the simplest case, the sound waveguide lies unprotected in the body. Then, with increased transmission losses due to lateral decoupling of Sound from the SWL in the surrounding body tissue to be expected. Usually these losses are too high. The SWL is therefore usually in a so-called. Probe tube out. The probe tube can be stiff or flexible. In this Probe tube may be z. B. to one of the many known medical Catheter or a medical endoscopic channel Catheters act, it may u. U. a simple tube in question.
The length of the SWL according to the invention is preferably at least 8 cm, but not more than 5 m. A length of more than 8 cm has several advantages, z. B. SWL can then additionally serve as a flow path, about a easier separation of the reflected signal from the incident signal to allow (eg in transient and decay processes). A length of fewer than 8 cm is hardly necessary even in medical applications. But if it can be set up, the length of the SWL should be at least 30 cm be, because then the handling of the probe is easier.
A length of 5 m is sufficient even for certain technical applications under extreme conditions, for example, if the probe head of strong irradiation or strong is exposed to thermal stress, completely off. At a length of more than 5 m SWL is usually hardly usable, mostly the dispersion and absorption of the sound pulses too strong or the repetition frequency The sound pulses must be due to the long duration of the sound pulses be reduced too much. The use of shorter SWL leads but in general to better features of the SWL. Therefore, if so it can be set up, for technical applications, the length of the SWL 3 m and less than 2 m for medical applications.
For the ultrasonic probe according to the invention are the most known Ultrasonic transducers and -Richtelemente suitable. More care must be taken be used on the selection of suitable sound waveguide.
From DE-OS 19 47 968 a SWL is known which thinner from a bundle (Carbon) fibers whose end surface is designed so that the bundle as a whole has a sound-focussing effect. An application for this fiber bundle is not specified. The disadvantages of fiber bundles in the application described above have already been discussed.
The transmission of sound continues investigations of the sound transmission predictive effects. Systematic considerations about elastic Waves in fibers or cylinders can be found in L. Pochhammer, "Über die Reproduction rates of small oscillations in an unlimited Isotropic Circular Cylinder ", J. Math. 81, 324 (1876), E. Sittig," Zur Systematik the elastic natural vibrations of isotropic circular cylinders ", Acustica 7, 175 (1957) and R.N. Thurstson, "Elastic rods and clad rods", J. Acoust. Soc. At the. 64, 1 (1978).
In US-PS 33 15 663 a bronchoscope is described that a SWL contains. With this SWL, sound waves of about 20 kHz are supposed to enter the bronchi be guided to solve stuck mucus there.
In US-PS 33 68 085 is called a "amplifier horn" Taper described, with the appropriate sizing sound waves in to couple a SWL. As materials for the taper are in the PS Although metals specified, in principle, the taper but also from others Materials exist, for. B. made of glass.
US-PS 37 36 532 describes SWL for low dispersion signal transmission. The waveguide is surrounded by sound absorbing layers around the Shield the sound wave. However, these layers strongly attenuate the guided ones Sound wave, because the evanescent wave penetrates into the absorber. In In another embodiment, surface or boundary waves are used Transmission of the sound wave used - such SWL work, however only at extremely high frequencies (the sound wavelength must be smaller its than the thickness of the layer leading to it). They are also flexible SWL known to have a core and a coat with different elastic Have properties, for. Example from US-PS 38 24 505 or 39 22 622. These SWLs are said to work like optical core-sheath fibers, i. H. the sound wave should be locked in the core and by the influences of the environment be isolated. For this, however, the thickness of the shell would have a multiple the sound wave length. With the typical dimensions flexible fibers would be very high frequencies necessary, one must of 100 MHz go out - for sonography these frequencies are too high.
Characteristic of the known SWL is also that in them the Sound waves are located in radial or azimuthal modes whose geometric Dispersion is small. But we found that these fashions are not Sound waves can transmit with higher power and that their inputs and Coupling is too difficult for the practice.
Optical fibers are also known for laser spectroscopic applications. be coupled into the optical and acoustic waves. By acousto-optical interactions between the waves will be the frequency of the optical wave shifted by an integer multiple of the acoustic wave. In order to achieve significant frequency shifts, the sound frequency However, be extremely high. The fibers, generally thin optical single-mode fibers, can only low sound power over short Transmit distances because they focus on the coupling and transmission of optical Waves are tuned.
The invention can be in principle with a variety of materials for realize the SWL. Advantageously, the selection of a suitable Materials are problem-dependent:
Many materials that z. B. due to their mechanical data theoretically Would have advantages (eg Beryllium with speed of sound of 12.5 km / s and the Poisson number of only 0.1 or the chalcogenide glasses with a very low ultrasound absorption) due to their toxicity or deficiency Machinability. SWL from beryllium, however, could be used for technical Applications in which a touch of the SWL is excluded, quite possible. In the medical field z. SWL from Au or Pt alloys, however, these materials usually have too low a strength. Copper, brass, bronzes u. Ä. are simple though However, they usually have a coarse-grained structure, which can lead to a considerable ultrasonic absorption (the mostly due to storage or aging); these materials are therefore usually because of unfavorable mechanical properties (besides the toxicity). Moreover, due to metallic SWL the electrical conductivity problems occur - in such cases would basically offer the use of SWL glass.
Those skilled in the art will be familiar with the dimensioning rules in this specification and due In his experience the materials suitable for a particular application for the SWL. Nevertheless, below are materials for SWL, with which the task is easiest to solve and with which almost all applications can be covered.
The most preferred material is silica glass (SiO₂ glass) as it is is used for the optical fibers. These are glass, up to insignificant admixtures of SiO, GeO₂, B₂O₃, P₂O₅ and TiO₂ exists. This glass shows the best data due to the sum of its Characteristics, such as the strength, elastic parameters, sound absorption and electrical resistance. It can be easily used in the medical field be used. The same applies to the conventional technical and optical glasses, which are also preferred as material for the SWL. The production of moldings or fibers with different profiles and dimensions with high accuracy of glass or silica glass is z. B. known from optical communications.
Tungsten and titanium alloys also have good properties, e.g. B. high strength and low ultrasonic absorption. Both materials can be used in the medical field without major problems. Steel, Mg and Al alloys (and other light alloys) Although overall poorer mechanical properties and a relatively high Ultrasonic absorption, but they are easier to process than W or Ti alloys. That's why they are also shortlisted taken from the SWL materials.
The SWL of the ultrasonic probe according to the invention has an outer diameter D, hereafter simply diameter larger than 20 microns and smaller than 1000 μm. For a SWL with non-circular cross-section is with Diameter of the azimuth angle ψ dependent chord D (ψ) of the SWL cross-sectional area denoted by the vertex of the angle ψ. The The vertex lies in the symmetry axis of the SWL (usual coordinate system). Then let the smallest value for D (ψ) be larger than 20 μm and the largest value for D (ψ) smaller than 1000 μm. This will ensure that SWL has sufficient strength and one for use in probe tubes or catheters has sufficient flexibility. Thinner SWL do not have sufficient tensile strength and thicker too high bending stiffness. With these dimensions, the SWL can still in the usual sense (as with the optical fibers) are called flexible.
The use of SWL of non-circular cross-section is preferred, such as when a torsional movement of the SWL, e.g. B. can increase the dispersion, should be suppressed. In SWL with a non-circular cross-section, the ratio of the maximum value D max to the minimum value D min should be at least 1.4, in particular for the chord D (ψ) dependent on the azimuth angle durch. This ensures that the SWL independently under the influence of a bending moment due to its direction-dependent bending strength twisted so that the bending of the SWL takes place about an axis which is parallel to the direction with the maximum value of the chord. In particular, it is advantageous that the directions with the maximum and the minimum value for the tendon are perpendicular to each other. Therefore, the bending stiffness of the SWL effective for this bend, which is then determined by the short tendon, is particularly low. This can be achieved that a SWL with a high strength, ie large cross-sectional area, yet has a small bending stiffness for the bend.
In general, however, SWLs of irregular cross section predominate the disadvantages. In SWL with non-circular cross section, there are z. Always Axes with an unfavorable ratio of bending stiffness to cross-sectional area. Regarding the direction with the low bending stiffness can then easily be excited Scher bending waves. In all applications, where z. B. the coupling of sound waves with torsion waves of is less important SWL are preferred with circular cross-section (except for manufacturing-related cross-sectional fluctuations). At a SWL however, with a circular cross-section one finds no axis with one lower bending stiffness. The SWL can therefore a total of less Have flexural rigidity. Therefore, for the SWL with circular Cross section a diameter D of less than 800 microns preferred.
For a SWL with circular cross section, a number of the in the Fiber optics known prefabricated components such as plugs, hoses, Feedthroughs, etc. applicable, if the SWL have standard sizes. In order to use these components, it is recommended that the Outside diameter of the SWL in the range of 60 microns to 600 microns moves.
The SWL of the ultrasonic probe according to the invention is intended for the transmission of Axial waves be suitable. For axial shafts, the SWL oscillates predominantly in Direction of its axis. As a result, a high input to the SWL ends can be achieved. and achieve coupling efficiency for sound waves. In addition, are in inventive Dimensioning and use of the SWL, the transmission losses by decoupling and the distortion of the sound pulses due to Dispersion low.
It is unavoidable that even with the axial shafts a movement of the SWL Material takes place in the radial direction: First, the axial movement always with a radial vibration of the SWL due to the transverse contraction connected to the material, on the other hand provide axial waves Borderline case of the so-called Axi-Radialwellen represents - Axialwellen can under unfavorable Conditions that are unfortunately present in typical applications, easily into another borderline case, called radial waves. Both Radial waves dominate the radial motion of the SWL (a type of shear waves). This will cause very strong sound energy from the SWL into the surrounding Medium coupled and attenuated the guided sound wave, or it finds one strong influence on the propagation states of the guided sound wave through the surrounding medium. The resulting additional disperison and pulse distortion is uncontrollable.
It has been found that these effects depend on the Poisson's number ν (transverse contraction number) depend on the fiber material. It was surprisingly that you have all the potential fiber materials in two categories into those with ν <0.20 (this includes SiO₂ with ν ≈ 0.17- 0.19, W alloys with ν ≈ 0.17 and Be alloys with ν≈0.10) and in those with ν0.20 (these include "normal" glasses with ν≈0.25 and "normal" metallic materials with ν≈0.29-0.36, depending on the processing, Pretreatment and alloy), for which one different Conditions found:
To avoid the radial movement (turning into radial waves), applies for the product of the SWL diameter D (for non-circular SWL the greatest value of the chord) and the carrier frequency f₀ of the sound waves:
D · f₀ 7000 m / s, if the SWL consists of materials whose Poisson number ν is less than 0.20,
D · f₀ 4200 m / s otherwise.
The SWL properties can be improved even further by using D · f₀- Product meets even lower limits (ie at a given Carrier frequency selects smaller values for the diameter). More preferred is therefore for SWL
D · f₀ 3000 m / s, if ν <0.20
D · f₀ 1700 m / s otherwise.
In SWL, which consist of several materials, it is in practice such that these materials have a similar Poisson number (eg SiO₂- Glasses with slightly different doping, alloys with less Variation within the same metal class) - otherwise the connection would be the materials do not have the required strength. you Therefore, the fiber materials usually a uniform Poisson number assign ν. If you still have a SWL, its mechanical Effective materials are very different, so in the o. a. Bemaßungsregel to consider the largest Poisson number.
Observing the above conditions (upper limits for D · f₀ as a function of ν) leads to the further positive effect that the difference between the group velocity of the waves and the phase velocity is negligibly small in practice. The phase velocity c a of the axial waves is then approximately
(c₀ = is the speed of sound for longitudinal waves in a thin one Rod; ν, E and ρ: Poisson's number, elastic modulus and density of the SWL material; for SWL, which are composed of several materials to set RMS values and the group velocity:
g ≈ c a ³ / c₀²
(for the phase and group velocity there are no closed ones Expressions). As a result, the calculation of sonographers will be easier, a decisive advantage for the practice.
Another advantage is that the coupling to surface or interface waves (eg Rayleigh or Lovewellen) becomes small. In contrast to known ultrasonic delay lines, the straight surface or Interface waves, it proved to be advantageous for the SWL to to prevent any coupling to these waves: surface or boundary waves are with a strong extraction and dispersion, in addition uncontrollably depends on the properties of the surrounding medium, connected. In these waves, the sound energy in a thin Layer of SWL material transported, they can not therefore the transmitted necessary sound power.
When coupling the sound, it may be difficult, pure To stimulate axial waves. Due to different ultrasonic impedances (eg for axial and shear waves, G: shear modulus) at transition points usually observed even at low sound power, perfect radial symmetry and perfect axial excitation, that always too Radial waves occur, albeit with significantly lower amplitude than at the axial waves. By deviations from the radial symmetry, z. B. production-related small tilting of components, strong bends or Buckling in the course of the SWL, usually arise, especially at higher Sound power, also shearing or bending waves in the SWL (again with clearly lower amplitude). Here it can be used positively that at the SWL invention, the radial, shear and bending waves by coupling are attenuated more than the axial waves, so that these waves are negligible for longer transmission distances. Should still A too strong excitation of these waves occur, usually helps a reduction the sound power. You can also attach devices to the SWL, specifically dampen radial, shear and bending shafts (below are those Devices for the shear bending waves described). Furthermore, you can also design the ultrasonic directors at the distal end of the ultrasound probe that only axial waves come into effect. This execution is especially recommended for short SWL.
The SWL of the ultrasonic probe according to the invention is intended for the transmission of Torsionswellen be suitable. In torsional waves the SWL oscillates in azimuthal Direction (cylindrical coordinates). They also make a guy of shear waves, the without transverse contraction or radial movement through the SWL is running, the Poisson number of the fiber material is for torsional waves without meaning. When dimensioning according to the invention and use of the SWL are the transmission losses and the distortion of the sound waves due to the Dispersion also low. For the transmission of torsion waves are SWL with circular cross-section preferred, because then the transmission losses by decoupling (or coupling to the surrounding medium) on are lowest.
The torsion waves may be degenerate, i. H. There may be several torsional modes occur at the same frequency. Because these torsional modes are similar Have symmetry properties, the sound energy between them easy to cross over. As a result of this mode coupling, the dispersion the torsional waves increase. Therefore, the SWL according to the invention with regard to the transmission of torsional waves in single-wavelength (monomode, only the Torsion fundamental is transmitted). Is to:
f₀ · D 14 000 m / s for SWL based on Be,
for D 6100 m / s for SWL made of silica glass and
f₀ · D 5100 m / s for SWL made of other materials
(smaller-than-equal relationship, f₀: carrier frequency of the sound waves, D: diameter the SWL). The differences for the upper limits for f₀ · D result itself from the strongly different sound velocities for the Torsional waves in the media.
In compliance with the above conditions, no dispersion occurs in a (stretched) SWL of approximately circular cross-section; ie the speed of sound of the fundamental torsion wave is independent of the frequency and is c t = (G: shear modulus, ρ: density of the fiber material, c t being the sound velocity of shear waves known from elementary mechanics). This is of particular advantage in the transmission of short sound pulses.
The higher order torsional waves show strong dispersion and are usually unsuitable for the transmission of short sound pulses.
The torsional fundamental wave, however, has the property that the azimuthal Movement of SWL increases from inside to outside, d. H. his azimuthal movement is the largest on the surface: The SWL material is used in the Torsion fundamental actually poorly exploited, the torsional fundamental is therefore for transmitting sound waves with higher power in usually less suitable than the axial shafts.
Especially when the SWL is in a highly viscous medium (For example, a rinsing fluid in a catheter) may be due to the strong azimuthal Movement of the SWL increased transmission losses occur. The experience shows that the coupling losses of a SWL for torsional waves can reduce when you reduce its diameter. That's why stronger preferably, the following applies:
f₀ · D 8000 m / s for SWL based on Be,
4200 m / s for SWL made of silica glass and
f₀ D 3000 m / s for SWL from all other materials.
The solution of the task requires the SWL to be precise to the applications vote. With the SWL according to the invention that is possible for applications in which investigations after the pulse echo method or after the Doppler method to be performed when the carrier frequency f₀ greater than 450 kHz and less than 28 MHz.
By restricting to the frequency range of more than 450 kHz is avoided that in case of disturbances of the ideal SWL course, z. B. at bends, the guided sound waves approximately (with excitation of axial waves) spontaneously in turn so-called bending waves. Flexible shafts are used to transmit sound waves unsuitable for the purposes of the invention, because they are too strong lateral motion associated with a strong damping and because of their Dispersion (sound velocity ≈) for the transmission of short Sound pulses is much too high. By restricting to frequencies less than 28 MHz will be coupling to surface or interface waves with the disadvantages described even more reduced.
For the transmission of sound waves in the frequency range from 800 kHz to 20 MHz, the ultrasound probe can be made particularly simple. At a Frequency of less than 800 kHz it could occur that at bends SWL has a deflection-dependent contribution to the speed of sound, because, for. B. the axial forces acting in the SWL axial forces a stationary Stimulate oscillation of the curved SWL segment. The bend-dependent Speed of sound for axial waves in the SWL according to the invention is approximately
c (f₀) ≈ c₀ (1 + 0.013 · (λ / R) ²)
(R: bending radius: λ: sound wave length in the fiber; λ ≈ c₀ / f₀, c₀: speed of sound in the stretched SWL. If the frequency is too low, can z. B. the duration of a sound pulse depends too much on the bending radius - in ultrasound technology, such little controllable Runtime effects hardly considered in the evaluation. Exceeds the Frequency 20 MHz, z. B. due to the short wavelengths the design of ultrasonic transducers with suitable input and output elements for the SWL difficult in practice.
The frequency range which can be covered by the SWL according to the invention is larger as necessary for medical sonography (about 1 to 20 MHz). Higher frequencies are not useful because then the attenuation of the ultrasonic waves would be too strong in biological tissue (the absorption coefficient Most fabric types for ultrasonic waves are approaching square with the frequency and is about 0.2. , , 2.5 dB / cm · (f₀ / MHz) ². Lower frequencies would not make sense, because the spatial resolution of the sonograph proportional to the sound wavelength and thus is reciprocal to the sound frequency (λ ≈ c₀ / f₀; the speed of sound c₀ of most tissue types is 1450 to 1650 m / s).
As a rule, the SWL should be flexible, ie. H. on one by the respective Application provided radius be bendable. A minimal flexibility of SWL is advantageous even when used in rigid probe tubes, z. B. because then the leadership of other elements in the probe tube is easier. In rigid probe tubes, a minimum bend radius is generally sufficient of 10 . , , 30 cm out. Flexible probes for engineering or medical applications but make much higher demands, here is a bending radius from 2. , , 5 cm, sometimes less than 2 cm. to Rough sizing of SWL, it is sufficient of relative stiff SWL, hereinafter "stiff SWL", with a minimum bending radius of R ≈ 10. , , 30 cm and of "bendable SWL" with a minimum bending radius of R ≈ 2. , , 5 cm to go out.
This results in further restrictions on the SWL diameter: On the surface of a radius R bent SWL made of a material with elastic modulus E (in SWL of several materials, the modulus of elasticity of the material of the outermost layer) with the diameter D (in SWL with non-circular Cross-sectional profile of the diameter in the plane, which contains the SWL tangent bending circle) is z. B. the normal stress (tensile or compressive stress in the direction of the SWL axis) σ max ≈ 0.5 · E · (D / R). This voltage is added to the voltages caused by the guided sound wave, but which are generally much lower than the bending stresses.
Of course, the resulting stress must be less than the flow, yield or breaking stress of the SWL material. For the SWL according to the invention, however, even narrower limits must be observed: σ max must be smaller than the maximum stress, up to which the material behaves elastically at all (small permanent deformation of the material after the voltages disappear), and for applications in which it depends on a particularly frequency pure transmission arrives, z. For example, in Doppler sonography, the stress should be even lower than the characteristic stress limit of the material to which the material behaves linear-elastic (up to which a linear relationship between stress and strain - Hooke's Law - is found). If this limit is exceeded, z. B. a frequency conversion (eg., Sum or difference frequency mixing) or overcoupling of sound energy to other modes occur.
Unfortunately, the limit to which a material behaves linear-elastic, out of focus: in the potential materials is also very low Strains observed a deviation from the linear-elastic behavior. On the other hand, this non-linearity usually does not have an immediate effect because, for. B. a bending-induced dispersion of sound waves occurs, which has a coherent interaction between different Sound modes or sound waves with different frequency prevented (no constructive overcoupling due to too short interaction length). A number of mechanisms have been found that describe the ones described Favor or prevent effects. You can not see the effects in the individual, but must apply simple rule of thumb.
In SWL from relatively ductile Ag, Au or Pt alloys (modulus of elasticity E for Ag: ≈ GPa, Au: 80 GPa and Pt: 173 GPa; 1 GPa = 10⁹ Pa) must the Bending stress on the SWL surface lower than 90 MPa (≈ 9 kp / mm²; 1 MPa = 10⁶ Pa). Therefore, these materials come only for stiff SWL (minimum bending radius of R ≈ 10 to 30 cm), for the SWL diameter a value of less than D <250 μm is preferred. Did you want bigger ones To reach fiber radii or to bend the SWL closer, one would have the materials alloying higher, then for these materials would be a higher ultrasonic absorption to accept.
In SWL made of Fe or steel alloys (modulus of elasticity E ≈ 210 GPa) the bending stress on the SWL surface should be lower than 180 MPa. That's why becomes for stiff SWL (R ≈ 10 .. 30 cm) the diameter D 200 μm and for bendable SWL (R ≈ 2 ... 5 cm) the diameter D 80 μm is preferred. In Although these materials is a higher tensile strength than precious metal alloys achieved because of the higher modulus occur at the surface such fibers but always high tensile stresses.
This applies even more to SWL made of W alloys (E ≈ 400 GPa). There, the bending stress at the SWL surface should be lower than 200 MPa his. Therefore, for stiff SWL (R ≈ 10 ... 30 cm), the diameter D becomes 200 μm and for deflectable SWL (R ≈ 2 ... 5 cm) the diameter D 50 μm is preferred. For W alloys, the production of very thin SWL is narrow Tolerances known.
In SWL made of Mg or Al alloys (E ≈ 40 ... 70 GPa) the bending stress should be at the SWL surface lower than 100. , , Be 120 MPa. That's why for stiff SWL (R ≈ 10 to 30 cm) the diameter D <300 μm and for bendable SWL (R ≈ 2 ... 5 cm) the diameter D <160 μm is preferred. With these materials makes the low modulus of elasticity positively noticeable. The relatively low breaking stress of these materials is not achieved because the tensile or compressive stresses on the SWL surface due to the low E-modulus are low.
In SWL made of Ti alloys (E ≈ 105 GPa), the bending stress at the SWL Surface be lower than 200 MPa. Therefore, for stiff SWL (R ≈ 10. , , 30 cm) the diameter D 300 μm and for bendable SWL (R ≈ 2 ... 5 cm) the diameter D 120 μm is preferred. At SWL makes from these materials positively noticeable that here a low modulus of elasticity and a high tensile strength meet.
In SWL made of glasses (normal technical or optical glass or silica glass, E ≈ 72. , , 80 GPa) should lower the bending stress at the SWL surface be as 500 MPa. Therefore, for bendable SWL (R ≈ 2 ... 5), the SWL diameter D 350 μm preferred. (For larger bending radii there are no restrictions.) In comparison with the metals was for glasses surprisingly found a much larger permissible SWL diameter. our This is considered to be due to the relatively low modulus of elasticity (the mechanical stresses are therefore low on the SWL surface) and attributable to the microscopic structure of the glasses: glasses have one homogeneous structure, whereas metals are polycrystalline. In metals can therefore be microscopic even at relatively low mechanical stresses Movements of microcrystallites take place (cracking of grain boundaries, Glides), which are impossible in glasses. That's why it is advantageous to make the SWL from glasses.
Due to the absorption of sound energy by the SWL material (intrinsic Sound absorption) occur transmission losses. At the end of the SWL Therefore, the sound signal can be attenuated so much that it is for the Measurement is no longer suitable. The intrinsic sound absorption of the SWL hangs the used SWL material, the transmission length L and the carrier frequency f₀ off.
Unfortunately, it is difficult to calculate the sound absorption coefficient of a material reliable predictions, it depends on many factors. at Polycrystalline materials occurs, for. B. attributable to scattering Contribution to (similar to Rayleigh scattering in electromagnetic radiation), proportional to the fourth power of the carrier frequency and proportional increases to the cube of the mean crystallite diameter. There z. B. in metals of the crystallite diameter by machining (about annealing) can be changed in a wide range, the ultrasonic absorption coefficient vary greatly. It may fluctuate the value for a material by more than three orders. The material technicians but it is known how to low on a material Sets ultrasonic absorption coefficient.
The SWL according to the invention is designed so that some contributions to the ultrasonic attenuation, in a massive piece of the material in question the sound wave length to the transverse dimensions so that the Rayleigh Scatter-like contribution to ultrasonic attenuation is small: the Scattering is not isotropic, but bundled into a narrow angular range around the SWL axis. The scattering amplitude is attenuated accordingly and the ultrasonic attenuation lower.
To simplify the design of the SWL can be found on the basis of empirical data following rule of thumb: To keep the sound absorption small, SWL preferred, the condition
L · f₀² K
suffice (f₀: carrier frequency, L: SWL length), whereby the material or SWL Constant K for SWL off
For silica glass, the best values are observed, u. E. That's up again its homogeneity traceable. Keeping these limits is enough for most use cases. But for high resolution sonography is u. U. an even lower ultrasonic absorption required; then should be for SWL off
be valid. Because of the high resolution required for high resolution sonography Sound frequencies must be assumed that then in the first place Silica glass fibers come into question.
It has been found that by coupling the axial shafts to shear bending shafts high transmission losses occur. Shear bending waves are namely associated with very strong movements of the SWL (it can be under unfavorable Conditions even whiplash watching), the highly elastic or stimulate viscous vibrations in the surrounding medium. Thereby the guided sound wave loses energy and becomes its dispersion increased. This effect occurs especially at low frequencies.
The occurrence of shear bending waves can usually be prevented if the lateral movement of the SWL is limited by support elements. For this purpose, the distance of the support elements L st along the SWL axis should be smaller than half the wavelength of the forming at the carrier frequency shear bending waves:
D is the diameter of a SWL with a circular cross-section or the minimum value of the chord through the cross-sectional area in a SWL with non-circular cross section (it is the shear bending waves with the shortest Wavelength, with respect to the lowest bending stiffness of the SWL or the smallest tendon, to take into account).
Under certain circumstances, no support elements can be attached. Then you have to losses incurred by the lateral movements of the SWL become. These may possibly be reduced by the fact that the transmitted Sound power is reduced: The tendency to couple the axial shafts namely on scher bending waves grows, if the sound power of Axial waves increases.
The support elements may in unfavorable cases have runtime interference effects occur for the axial waves. To suppress the, applies
Should the support elements described for damping the shear bending waves be attached and should be at bends of the probe tube of the SWL bent around a predetermined axis, it is further advantageous that To perform supporting elements so that they bend the sound waveguide to force the predetermined axis. This will reduce the total number of Support elements of the SWL reduced, which ultimately resulted in a higher Transmission efficiency of the SWL. In SWL with non-circular Cross-section can be achieved by supporting elements that at bends of the probe tube of the SWL is bent about an axis parallel to the direction with the greatest value for the tendon D (ψ).
In SWL for the transmission of sound pulses, the formation of shear bending waves with heavy losses can be prevented by the lateral movement of the SWL also that within the interaction length between the waves no structural reinforcement of the shear bending waves can take place. If T p is the pulse duration of the coupled-in sound waves, then this should be preferred
be valid. This effect can be understood if one assumes that the maximum interaction length between axial and shear bending waves the difference speed multiplied by the pulse duration is determined by these waves. The specified relationship ensures that this interaction length is so short that no effective overcoupling of sound energy from axial waves to shear bending waves takes place.
In SWL for the transmission of short ultrasound pulses, the difficulty arises on that the impulses are spread by the transmission. When The reason for this was a dependence of the spectral sound velocity (which is not detected by the group velocity, but by "higher Order ") is detected by the SWL geometry This effect occurs especially for the higher order torsional waves, they are therefore for Transmission of short sound pulses usually unsuitable. Both but single-wave SWL invention is, as stated above, the Torsion fundamental wave dispersion-free - with them is therefore hardly with Difficulty in the transmission of short sound pulses to count.
In the axial shafts of the invention SWL occurs only one weak dispersion; this can be further reduced,
- i) if the SWL geometry is as even as possible (SWL with a circular Cross section are therefore advantageous in this respect) or
- (ii) if the SWL is made of materials differing in their mechanical properties Properties (elasticity modulus, shear modulus, Poisson's value and density) as far as possible little different, so the SWL is homogeneous.
Therefore, for applications where there is a slight broadening the sound pulses arrive, SWL from a homogeneous material with circular cross-section is preferred.
These effects can also be avoided if the following conditions for the pulse duration T p of the sound pulses, the SWL length L (transmission length between transducers and straightening elements), the SWL diameter D (maximum diameter at SWL with non-circular cross-sectional profile) and the carrier frequency f₀ is complied with:
for SWL on a Be basis
for SWL on silica glass or W alloys
and for SWL from other materials
(greater-equal relationship, the values on the right have the dimension Seconds³ divided by meters³). That for Be-, silica glass or Tungsten-SWL smaller values are allowed, can be returned to the low Attributed Poisson number.
By maintaining these values, it is ensured that the broadening of the ultrasound pulses due to the transmission is significantly smaller than the duration of the ultrasound pulses T p . That's enough for most cases in practice. For applications with the highest resolution, however, even higher requirements could occur. It could be z. B. be necessary that the broadening of the sound pulses even in comparison with the duration of an oscillation of the sound wave (≈1 / f₀) is short. Then, the previously specified condition is generally no longer sufficient, and it should
for SWL on a Be basis
for SWL on silica glass or W alloys
and for SWL from other materials
be valid. To comply with even higher values is for no realistic application required.
If necessary, the SWL can be made from a fixed protective cover be surrounded by one or more layers. The protective cover protects the SWL against chemical effects by the surrounding medium (eg atmosphere, Body or rinsing fluids) or avoids scratches in the SWL interface z. B. by an awkward handling. In accordance with the invention Design, the protective cover has a negligible influence on the mechanical properties of the SWL and its ability to Guidance of sound waves.
The application of this protective cover is particularly recommended for SWL Glass, because with these brittle materials already microscopic scratches on the SWL surface significantly reduce the strength of the SWL. The protective cover can z. B. from a (ductile) plastic, such as in the fiber optics used UV-curable acrylates, silicones or polyimides (then the SWL can be sterilized at high temperatures) or a thin one Metal layer exist.
When SWL made of metallic materials can usually on the protective cover be waived. But if a protective cover should be applied, for example made of gold for the chemical inerting of the SWL, it is recommended, one to use the many known electrolytic process.
In the SWL of glass according to the invention may be in principle to the be in the optical communication known optical fibers. The embodiment of the SWL according to the invention as an optical fiber can be considerable Have advantages:
The optical fiber can, for. B. transmitted light energy, which serves in an endoscope designed as an ultrasound probe to illuminate the targeted object.
By transmitting optical signals with the SWL, its state can be controlled during operation and a break detected quickly and without disassembly of the probe.
When using an optical fiber as SWL, it is preferred that it be is a step index fiber (core-clad fiber). For fibers based on silica glass core core fibers of the core may consist of pure SiO₂, which is surrounded by a weakly F-doped SiO₂ jacket, wherein the F doping the refractive index reduction necessary for optical beam guidance of the jacket with respect to the core. The F-doping is in the rule so low that the mechanical properties of the SiO 2 glass only be adversely affected.
With an F-doping but only a small refractive index difference can be between the core and the sheath of the fibers. The resulting numerical aperture of the fibers may be too small to capture sufficient radiation at the coupling end to the targeted object at the coupling end to illuminate sufficiently strong. Then it recommends to manufacture the fibers as core-sheath SWL from multi-component glasses. It should be noted that when pulling these fibers no mechanical stresses in the fiber are "frozen". These tensions can z. B. their cause in different coefficients of thermal expansion of the core and the cladding glass. The glass manufacturers It is known which glasses are to be selected, so that in the case of the drawn The mechanical stresses between the core and the sheath are low are.
The SWL may have an axially variable cross-section. In particular, it is considered that the cross-section or decoupling end for the sound waves changes and in the long middle part in the is essentially constant. When changing the cross section, it can is an expansion of the SWL ("taper") to the coupling or decoupling sound waves into and out of the SWL.
It is recommended that the diameter D (or the largest tendon through the Cross section in non-circular cross section) of the expanded portion of the SWL is smaller than the sound wave length of the axial waves (λ = c₀ / f₀): D <λ. This ensures that when passing the Tapers the in the SWL according to the invention in itself very even wavefronts the Sound waves in SWL are only slightly deformed, d. H. then there is the Coupling of the axial shafts to radial shafts negligible.
The SWL according to the invention should primarily serve the sound waves of an ultrasonic transducer located at the proximal end of the probe to transmit a located at the distal end straightening element (irradiated Sound signals). But it can also serve the purpose of one Ultrasound receiver at the distal end received sound waves to one to transport electroacoustic transducers at the proximal end of the probe. Optionally, this transducer is identical to the transducer that irradiated the Has generated signals. The ultrasonic receiver may be act to the ultrasonic straightening element that also for the transmission of the Sound signals is used. For the outward and return transmission can then the same Serve SWL. The ultrasonic straightening element for the transmission of sound waves and the ultrasonic receiver but can also separate components his. Then usually different SWL for the round-trip transmission used the sound waves.
The SWL can divide in its course, so that it is possible with to operate the ultrasonic transducer a plurality of ultrasonic directing elements.
Several initially separate SWLs can be combined to form a common SWL, so that it is possible with several separate ultrasonic transducers to supply a straightening head (but the SWL can also split again and lead to several converters). This arrangement has advantages
- - if a transducer with several distinct sound frequencies to be supplied, because the optimized in the usual sense ultrasonic transducers are tuned to a fixed frequency or
- - if a straightening element in multi-pulse operation with short pulses and should be operated at high repetition rate, because the production the sound pulses with the separate transducers technically easier is.
For simplification were usually devices for medicine (examinations from patients, tissues), although similar devices in the Technology (examination of objects, non-destructive material testing) can be applied. It is considered as included in the invention, that the SWL for the transmission of sound energy also in the art application can find.
It is included in the invention that it is in the inventive Ultrasound probes around flowmeters, in particular so-called. Intravascular or perivascular "flow meters" for medical applications. Such flow meters can use the Doppler principle, the "transit-time principle" (mono- and bidirectional) or according to the "multi-element principle" (with the flow mitbewegte inhomogeneities pass several in the flow direction successive ultrasonic registration elements; from the temporal Sequence of the registration pulses is the speed of the flow determined) work. In the known flow meters are the Ultrasonic transducer directly to the designated as coupling points straightening elements (see US-PS 42 57 275 for a flow meter after the multi- Elements principle or the US-PS 42 27 407 for a flow meter after the Transit-time principle), with the disadvantages described above. In the inventive Flow meters will use the coupling points via SWL connected spatially separated transducers.
For a sonograph for medical applications (transuminal guided probe for the intravascular determination of the plaque thickness of arteries, such as the A. poplitea), sonic pulses with a carrier frequency of f = 7.5 MHz and a pulse duration of T p = 533 ns (FIG. Wave trains with 4 periods) are transmitted with an inventive SWL. In biological tissue, the sound pulse within the pulse duration lays about 80 microns, which corresponds approximately to the depth resolution of the sonograph. This depth resolution is sufficient, according to the current state of knowledge for the intended application - also a better resolution would require a higher carrier frequency, but then would be expected with a much higher sound absorption (especially in calcified tissue). The repetition frequency of the sound pulses is 240 Hz. The peak power of the sound pulses is 40 W and is thus relatively high (despite the low average power of about 0.5 mW). The necessary transfer length from the extracorporeal transducer to the probe head inserted into the body is 75 cm. The fiber should be bendable with a radius of R = 2 cm ("bendable SWL").
It becomes a simple embodiment, a fiber of pure silica glass with circular cross-section, chosen. The diameter of the fiber (the Glass body of the fiber, the mechanically effective zone) is 62.5 microns. For The fiber is thus many components (plugs, bushings, seals etc.) usable in communications engineering for single-mode optical fibers be used. It is not for a transluminal probe necessary to design the SWL as an optical fiber (although with silica glass fibers it is obvious to use optical fibers) that can SWL consist of a homogeneous material. The SWL (the fiber) is but with a thin protective cover made of a UV-curable acrylate, like it is common in optical fibers.
Axial shafts are coupled into the SWL. The product of the carrier frequency the sound waves and the diameter of the fiber is 469 m / s. The Wavelength for sound waves with the o. Ä. Carrier frequency is 773 microns (In silica glass, the speed of sound for axial waves is 5800 m / s). The ratio of the fiber diameter and the sound wave length is relatively low, it is relatively strong Dispersion to be expected. For the inventive SWL we find for the relevant "dispersion parameter"
this is just the lower value of the range, the low dispersion SWL features.
For the SWL, the product is the length and the square of the carrier frequency L · f₀² = 4.2 · 10¹³ m / s², the intrinsic sound absorption of the Silica glass is therefore negligible.
The proposed SWL is mechanically flexible enough to fit in one free endoscopic channel of a transluminal catheter to be inserted. He is still sufficiently stiff to be introduced without kinking to be able to; There are no support elements required.
The coupling of the axial shafts to shear bending waves is weak; for the Parameter defining the interaction length for constructive overcoupling of Sound energy between these waves can be found
For such an ultrasonic probe suitable directional elements describes z. For example, US-PS 45 08 122, suitable converter based on Piezoceramics can be found z. B. in DE-OS 12 07 123.
that the diameter D of a sound waveguide with a circular cross-section or the maximum value D max and the minimum value D min of the chord through the cross-sectional area of a sound waveguide SWL with non-circular cross section between 20 microns and 1000 microns and
that for the product of the diameter D of a sound waveguide SWL with circular cross-section and the maximum value D max (then D = D max ) of the chord through the cross-sectional area of a sound waveguide with non-circular cross-section and the carrier frequency f₀ of the sound waves applies: D · f₀ 7000 m / s, if the sound waveguide SWL consists of materials whose Poisson number ν is less than 0.20, and
D · f₀ 4200 m / s for other materials, if axial shafts are to be transmitted, and: D · f₀ 14 000 m / s for SWL based on Be,
D · f₀ 6100 m / s for SWL made of silica glass and
D · f₀ 5100 m / s for SWL made of other materials, if torsional shafts are to be transmitted.
D · f₀ 1700 m / s is for other materials, if axial shafts are to be transmitted, and: D · f₀ 8000 m / s is for SWL on a Be basis,
D · f₀ 4200 m / s is for SWL made of silica glass and
D · f₀ 3000 m / s is for SWL of other materials, if torsion waves are to be transmitted.
- - 250 μm, if it consists of Ag, Au or Pt alloys,
- - 200 μm, if it consists of W, Fe or steel alloys,
- - 300 microns, if it consists of Al or Mg alloys, or
- - 300 microns, if it consists of Ti alloys.
- - 80 μm, if it consists of Fe or steel alloys,
- - 50 μm, if made of W alloys,
- - 160 microns, if it consists of Al or Mg alloys and
- - 120 μm, if it consists of Ti alloys or
- - 350 microns, if it is made of glass.
K = 2.2 · 20¹³ m / s² for sound waveguides made of Ag, Au or Pt alloys,
K = 7.0 · 10¹² m / s² for sound waveguides made of Fe or steel alloys,
K = 8.0 · 10¹³ m / s² for sound waveguides made of normal glasses and
K = 1.0 · 10¹⁶ m / s² for silica fiber glass waveguides.
K = 3.0 · 20¹² m / s² for sound waveguides made of Al or Mg alloys,
K = 0.7 · 10¹² m / s² for acoustic waveguides made of Ag, Au or Pt alloys,
K = 1.4 · 10¹¹ m / s² for sound waveguides made of Fe or steel alloys,
K = 8.0 · 10¹¹ m / s² for sound waveguides made of normal glasses and
K = 1.0 · 10¹⁵ m / s² for silica fiber glass waveguides.
Priority Applications (1)
|Application Number||Priority Date||Filing Date||Title|
|DE19914103145 DE4103145C2 (en)||1991-02-02||1991-02-02|
Applications Claiming Priority (2)
|Application Number||Priority Date||Filing Date||Title|
|DE19914103145 DE4103145C2 (en)||1991-02-02||1991-02-02|
|US07/830,157 US5294861A (en)||1991-02-02||1992-02-03||Ultrasonic probe|
|Publication Number||Publication Date|
|DE4103145A1 DE4103145A1 (en)||1992-08-13|
|DE4103145C2 true DE4103145C2 (en)||1993-06-17|
Family Applications (1)
|Application Number||Title||Priority Date||Filing Date|
|DE19914103145 Expired - Fee Related DE4103145C2 (en)||1991-02-02||1991-02-02|
Country Status (2)
|US (1)||US5294861A (en)|
|DE (1)||DE4103145C2 (en)|
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